ABSTRACT Air quality, ecosystem exposure to nitrogen deposition, and climate change are intimately coupled problems: we assess changes in the global atmospheric environment between 2000 and 2030 using 26 state-of-the-art global atmospheric chemistry models and three different emissions scenarios. The first (CLE) scenario reflects implementation of current air quality legislation around the world, while the second (MFR) represents a more optimistic case in which all currently feasible technologies are applied to achieve maximum emission reductions. We contrast these scenarios with the more pessimistic IPCC SRES A2 scenario. Ensemble simulations for the year 2000 are consistent among models and show a reasonable agreement with surface ozone, wet deposition, and NO2 satellite observations. Large parts of the world are currently exposed to high ozone concentrations and high deposition of nitrogen to ecosystems. By 2030, global surface ozone is calculated to increase globally by 1.5 +/- 1.2 ppb (CLE) and 4.3 +/- 2.2 ppb (A2), using the ensemble mean model results and associated +/-1 sigma standard deviations. Only the progressive MFR scenario will reduce ozone, by -2.3 +/- 1.1 ppb. Climate change is expected to modify surface ozone by -0.8 +/- 0.6 ppb, with larger decreases over sea than over land. Radiative forcing by ozone increases by 63 +/- 15 and 155 +/- 37 mW m(-2) for CLE and A2, respectively, and decreases by -45 +/- 15 mW m(-2) for MFR. We compute that at present 10.1% of the global natural terrestrial ecosystems are exposed to nitrogen deposition above a critical load of 1 g N m(-2) yr(-1). These percentages increase by 2030 to 15.8% (CLE), 10.5% (MFR), and 25% (A2). This study shows the importance of enforcing current worldwide air quality legislation and the major benefits of going further. Nonattainment of these air quality policy objectives, such as expressed by the SRES-A2 scenario, would further degrade the global atmospheric environment.

[Show abstract][Hide abstract]ABSTRACT: Spatio-temporally consistent O3 doses are demonstrated in adult Fagus sylvatica from the Kranzberg Forest free-air fumigation experiment, covering cross-canopy and whole-seasonal scopes through sap flow measurement. Given O3-driven closure of stomata, we hypothesized enhanced whole-tree level O3 influx to be prevented under enhanced O3 exposure. Although foliage transpiration rate was lowered under twice-ambient O3 around noon by 30% along with canopy conductance, the hypothesis was falsified, as O3 influx was raised by 25%. Nevertheless, the twice-ambient/ambient ratio of O3 uptake was smaller by about 20% than that of O3 exposure, suggesting stomatal limitation of uptake. The O3 response was traceable from leaves across branches to the canopy, where peak transpiration rates resembled those of shade rather than sun branches. Rainy/overcast-day and nightly O3 uptake is quantified and discussed. Whole-seasonal canopy-level validation of modelled with sap flow-derived O3 flux becomes available in assessing O3 risk for forest trees.

[Show abstract][Hide abstract]ABSTRACT: The impact of climate change has been significant enough to endanger human health both directly and indirectly via heat stress, degraded air quality, rising sea levels, food and water security, extreme weather events (e.g., floods, droughts, earthquakes, volcano eruptions, tsunamis, hurricanes, etc.), vulnerable shelter, and population migration. The deterioration of environmental conditions may facilitate the transmission of diarrhea, vector-borne and infectious diseases, cardiovascular and respiratory illnesses, malnutrition, etc. Indirect effects of climate change such as mental health problems due to stress, loss of homes, economic instability, and forced migration are also unignorably important. Children, the elderly, and communities living in poverty are among the most vulnerable of the harmful effects due to climate change. In this article, we have reviewed the scientific evidence for the human health impact of climate change and analyzed the various diseases in association with changes in the atmospheric environment and climate conditions.

[Show abstract][Hide abstract]ABSTRACT: Trace metals and broad-spectrum antibiotic drugs are common environmental contaminants, the importance of which is increasing due to global climate change-related effects.
In the present study, the biological model organism E. crassus was first acclimated to five temperatures, from 25 °C to 33 °C, followed by exposure to nominal concentrations of copper, the antibiotic model compound oxytetracycline and mixtures of both, at increasing thermal conditions. Variations of temperature-related toxicity were assessed by two high-level endpoint tests, survival and replication rates, and two sublethal parameters: endocytosis rate and lysosomal membrane stability. The selected toxicants presented opposite behaviours as the protozoa's survival rates increased following an increasing thermal gradient in the oxytetracycline-related treatments, and a decline of tolerance in metal-related treatments was observed. Results of tests combining binary mixtures of tested toxicants showed a complex pattern of responses.

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deposition of nitrogen and sulfur, damaging eutrophicationand acidification of ecosystems and loss of biodiversity (3,4).In this work we evaluate the effect of changing emissionsand climate on ozone air quality, radiative forcing, andnitrogen deposition to ecosystems for the year 2030. We usea recently developed set of emission scenarios (5) for CH4,NOx, NH3, CO, SO2, and NMVOC, which differ substantiallyfrom the previous SRES scenarios (6). In the past few yearsincreasingairpollutionindevelopingcountrieshasbecomeapublicconcern((5)andreferencestherein).Consequently,many of the major rapidly developing countries in Asia andLatin America have issued legislation requiring emissioncontrols. Upon implementation, these regulations will sig-nificantlycaptheairpollutionemissionsattheregionalandglobalscales.ThisisthebasisofourCLE(CurrentLEgislation)scenario. Further, we evaluate the effects of the emissionsof a MFR (maximum technologically feasible reduction)scenarioandcontrastitwiththepessimisticSRESA2scenario.These emission scenarios were used internationally, by 26establishedglobalatmosphericchemistry-transportmodels(CTMs) driven by analyzed meteorological fields or generalcirculation models (GCMs). Although some models sharesubcomponents,theensembleofmodelresultsissufficientlybroad to estimate uncertainties resulting from the variousassumptionsinthemodels.Themodelsperformedbaseline(year2000)and2030scenarios,allusingafixedmeteorologyrelevant for the year 2000; a subset of models repeated the2030 CLE scenario but with a changed climate. In this paperwe give an integrative overview of the findings; otherpublications (7-10) present more detailed results from thislarge model exercise.MethodsUptofivesimulationswereperformedbyeachmodel(Table1): B2000evaluatedthereferenceyear2000,whileCLE,MFR,and A2 assessed the year 2030. We show in the SupportingInformation the importance of emission controls in the CLEandMFRscenarioascomparedtoSRESA2.ToavoidexcessiveequilibrationtimesofCH4weprescribedglobalCH4volumemixing ratios, using consistent values from earlier transientsimulations for 1990-2030 described in refs 5 and 11. GCMsperformed 5-10 years of simulations, using a climateappropriate for the time period 1995-2004. To evaluate theimpacts of climate change, an additional simulation(CLE2030c)wascomputedby10oftheGCM-drivenmodels,usingaclimateappropriatefor2030.Mostmodelersappliedthe IS92a climate scenario associated with a global meansurface warming of about 0.7 K between 2000 and 2030. Inthe Supporting Information we present the 26 participatingmodels, including characteristics of their resolution, chem-istry and transport parametrizations, and key publications.Compared to earlier IPCC modeling exercises (2, 12) twiceasmanymodelsparticipatedinthisstudy;modelcomplexity(inclusion of NMVOC chemistry) and resolutions haveincreased: half of the models had horizontal resolutions of2°-3°orbetter,andmostoftheothermodelshadresolutionsaround 4°-5°. In the following discussion we focus on theunweightedensemblemeanofthemodelresults,expressingthe variability of the results as the (1 σ standard deviation.We note that the (1 σ interval should be interpreted as alowerboundformodeluncertainty,whichcontainsadditionalunquantifiedprocesses.Ingeneral,wefoundrelativelysmall(<10%)differencesbetweenmeanandmedianmodelresults.ResultsSurfaceOzone.InFigure1a-dwedisplaytheensemblemeanannual average surface O3for B2000 and O3differences forCLE, MFR, and A2 in 2030. Figure 1a shows that calculatedannual average ensemble mean surface O3ranges from 40to50ppboverlargepartsofNorthAmerica,SouthernEurope,and Asia. Background values are 15-25 ppb in large parts oftheSouthernHemisphere(SH).Averagesurfacemixingratiosare 33.7 ( 3.8 ppb and 23.7 ( 3.7 ppb (Table 2), for theNorthern Hemisphere (NH) and SH, respectively. In Figure1a we also give averaged measurements for the year 2000.Our analysis reveals that our mean model results are within5 ppb of the measurements in the United States, China, andCentral Europe and may overestimate the measured annualaverageby10-15ppbinAfrica,India,andtheMediterranean.The reason for this overestimate is not clear but may berelatedtooverestimatesofNOxorNMVOCemissionsintheseregions. Also, the regional representativeness of the sparsemeasurements may be poor, and measurement precisionmayalsoplayarole.Theseissuesarecurrentlyunderfurtherinvestigation.The CLE scenario (Figure 1b, Table 2) would approxi-mately stabilize O3in 2030 at 2000 levels in parts of NorthAmerica, Europe, and Asia. However, O3 may increase bymore than 10 ppb in areas anticipated to experience largeemission increases in the transport and power generationsectors (e.g. India). Background O3increases by 2-4 ppb inthe tropical and mid-latitude NH related to worldwidechanges in CH4, NOx, CO, and NMVOC emissions. Theincreases are most consistently predicted in Asia, whereasthe ensemble predictions have large standard deviations inNorth and South America, Southern Africa, and the MiddleEast. A cleaner future is possible, if all currently availabletechnologies are used to abate O3precursor emissions. Inthis MFR case (Figure 1c; Table 2) O3decreases by 5-10 ppbin the most polluted regions. The models are consistent intheir prediction of surface ozone reductions with relativestandard deviations of 30-40%. Finally, consistent withprevious studies (2), in the A2 scenario (Figure 1d), annualaverage surface O3 increases by 4 ppb worldwide and by5-15 ppb in Latin America, Africa, and Asia.How is climate change expected to influence these O3changes?Theaverageresultsfrom10modelsfortheCLE2030cscenario shown in Figure 1e indicate that climate changemay reduce surface O3by 1-2 ppb over the oceans and by0.5-1ppboverthecontinents,althoughsomeregions,suchas the Eastern United States, may experience increases.TABLE 1. Overview of Simulations, Prescribed Methane Volume Mixing Ratios, and Global Anthropogenic Emissions of CO, NMVOC,NOx, SO2, and NH3asimulation meteorologydescriptionCH4[ppb]CONMVOCNOx(NO2) SO2NH3S1-B2000S2-CLE/CLEcS3-MFRCTM 2000 GCM SSTs 1990s baselineCTM 2000 GCM SSTs 1990s IIASA CLE 2030, current legislation scenario 2088CTM 2000 GCM SSTs 1990s IIASA MFR 2030, maximum feasiblereduction scenarioCTM 2000 GCM SSTs 1990s SRES A2 2030, the most ‘pessimistic’IPCC SRES scenarioS5c-CLE2030c only GCM SSTs 2030s IIASA CLE 2030 + climate change1760 977.0904.1728.7147.1145.5104.4124.8 111.1 64.8141.1 117.6 84.876.0 35.8 84.81760S4-A2 2163 1268.2 206.7206.7 202.3 89.22012904.1145.5141.1 117.6 84.8aEmissions in Tg full molecular weight/year. Additional information is found in the Supporting InformationVOL. 40, NO. 11, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY93587

assess the effect of large scale changes of ozone backgroundconcentrations calculated with global models. Note thatSOMO35 is also rather similar to the widely used metric,AOT40, which evaluates the accumulated exposure ofvegetation to ozone levels above 40 ppb.Figure2a-cgivesSOMO35forB2000,CLE,andMFR,andin Table 2 we give a regional analysis of SOMO35. No limitvalues have been established for SOMO35, but a thresholdof ∼3000 ppb days is consistent with air quality limitscurrentlyinuseinNorthAmericaandEurope(8).Accordingto our model calculations this threshold (yellow and redcolors) is exceeded in large parts of the world in the year2000, most notably in the United States, the Middle East,and South Asia. In the CLE scenario this situation isaggravated especially in South Asia due to a large growth ofemissions from the transport sector. Our model resultsindicate that the more polluting SRES A2 scenario wouldcompromise attainment of any existing air quality standardin most industrialized parts of the world by 2030. Only theMFR scenario predicts that ozone in all regions will be at orbelow the current air quality standards. The large scaleregionalandannualaveragedozoneandSOMO35arehighlycorrelated (r)0.99).Radiative Forcing from Tropospheric Ozone. In Table 2we present regional changes in tropospheric column ozone[Dobson units; DU] resulting from the emission scenarios.The current global average tropospheric ozone column iscalculated to be 33 ( 5 DU in close agreement with IPCC(1),with regional averaged values in the Northern Hemisphererangingfrom32to42DU.ComparedtothesimulationB2000,FIGURE 2. Ensemble mean SOMO35 [ppb days] (a) in the year 2000; (b) 2030 CLE; and (c) 2030 MFR.35909ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 11, 2006

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theglobaltroposphericozonecolumnincreasesby1.7(0.5and 4.3 ( 1.2 DU for CLE and A2 and decreases by -1.4 (0.4DUforMFR.Climatechange(CLE2030c-CLE2030)leavesglobaltroposphericozonerelativelyunaffectedwithachangeof -0.2 ( 0.6 DU. The impact of emission reductions andincreases is relatively uniform for MFR and A2, whereas theCLE scenario amplifies the regional contrast in the ozonecolumnsandhencepossibleclimateimpacts.Wefindglobalradiative forcings increments of 63 ( 15 and 155 ( 37 mWm-2for CLE and A2, respectively, and reductions of -45 (17mWm-2forMFR(10).Increasesinforcingscanbeashighas 300 mW m-2in Asia. We calculate that the sum of the O3and CH4radiative forcings, in the CLE and A2 simulations,contributes 23% and 29%, respectively, to the forcings ofCO2alone,whereasMFRwouldimplyasmalldecreaseof5%(10).Nitrogen Deposition. It is currently thought that 1000mgNm-2yr-1isathreshold(“criticalnitrogenload”),abovewhichchangesinsensitivenaturalecosystemsmayoccur(4,14). So far most studies have focused on the effects of NOydeposition (15), since it is intimately associated with O3formation.InFigure3awegivethecalculatedNOydepositionFIGURE 3. Ensemble mean (a) NOytotal deposition [mg N m-2yr-1] in 2000, (b) total reactive nitrogen (dNOy+NHx) deposition [mg N m-2yr-1] in 2000, and (c) MFR 2030 NOytotal deposition.VOL. 40, NO. 11, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY93591

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(NOy) NO + NO2+ NO3+ 2N2O5+ HNO3+ particulateinorganicNO3andorganicnitrates)intheyear2000,showingthat NOy deposition alone leads to an exceedance of thisthreshold in parts of the Northeast United States, Europe,andChina.NHxdeposition,relatedtoemissionsfromanimaland food production systems, may double the depositionfrom NOy. In 2000 the deposition of total reactive nitrogen(dNOy+NHx) exceeds 2000 mg Nm-2yr-1in extended partsof the world, including biodiversity hotspots (Figure 3b). Todate,theconsequencesforbiodiversityandecosystemhealthhaveonlybeenstudiedfortemperateregions,butithasbeensuggested that increased nitrogen deposition will play animportant future role in the decrease of plant diversityworldwide(16).AcomparisonofthecorrespondingcalculatedwetdepositionfluxeswithmeasurementsintheUnitedStates,Europe, Southeast Asia, Africa, and South America yieldsagreement within a factor of 2 for 70-80% of the measure-mentstations.ExceptionsareAsia,wherethemodelsstronglyunderestimate NOy deposition by up to 60%, and SouthAmerica, where almost no measurement data were found.In 2030, considering the CLE scenario NOy depositiondecreasesinEuropeby30-50%(notshown),isnear-constantin North America, and strongly increases in Asia by 30-100%. NHxdeposition increases almost everywhere by 50-100%,exceptinEurope.OurcleanMFRscenario(Figure3c),which was evaluated only for NOy, considerably improvesthissituation,withNOydepositionalmosteverywherebelow500 mg N m-2yr-1. In contrast, the A2 scenario in the year2030 leads to extended regions exposed to NOydepositionlarger than 1000 mg N m-2yr-1. The CLE and A2 scenariosproject further increases in nitrogen critical loads, withparticularly large impacts in Asia where nitrogen emissionsand deposition are forecast to increase by a factor of 1.4(CLE) to 2 (A2). We calculate (7) that at present 10% of thenatural terrestrial ecosystems receive nitrogen inputs above1000 mg N m-2yr-1. These percentages increase by 2030 to16% (CLE), 11% (MFR), and 25% (A2). We note that we didnot determine maximum feasible emissions reductions forNH3; instead we used in scenario S3-MFR the CLE NH3emissions.Comparison with Satellite Observations of NO2 Col-umns. Recent satellite observations allow us to evaluatenitrogen pollution on near global scales. For the year 2000,the GOME instrument aboard the ERS-2 satellite pro-vides a unique opportunity to compare model calculatedNO2 columns with measurements. We sample modelNO2 columns at the satellite overpass time (10:30 LT).Daily tropospheric NO2 column densities were calculatedby 17 different models; uncertainties in the retrievals arequantified by using three different retrieval algorithms (9).FIGURE 4. (a) Modeled and (b) GOME measured annual average NO2columns for the year 2000. Modeled data represent an average of17 models, and the GOME retrieval is an average of three retrieval products. For a consistent comparison, the data in both cases havebeen smoothed to a horizontal resolution of 5° × 5°.35929ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 11, 2006